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applied cryptography - protocols, algorithms, and source code in c

Because it is implemented in a finite state machine

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Unformatted text preview: etwork applications. In a secure network environment, for example, a terminal must be able to transmit each character to the host as it is entered. When data has to be processed in byte-sized chunks, CBC mode just won’t do. Previous Table of Contents Next Products | Contact Us | About Us | Privacy | Ad Info | Home Use of this site is subject to certain Terms & Conditions, Copyright © 1996-2000 EarthWeb Inc. All rights reserved. Reproduction whole or in part in any form or medium without express written permission of EarthWeb is prohibited. Read EarthWeb's privacy statement. To access the contents, click the chapter and section titles. Applied Cryptography, Second Edition: Protocols, Algorthms, and Source Code in C (cloth) Go! Keyword Brief Full Advanced Search Search Tips (Publisher: John Wiley & Sons, Inc.) Author(s): Bruce Schneier ISBN: 0471128457 Publication Date: 01/01/96 Search this book: Go! Previous Table of Contents Next ----------- In CFB mode, data can be encrypted in units smaller than the block size. The following example will encrypt one ASCII character at a time (this is called 8-bit CFB), but nothing is sacred about the number eight. You can encrypt data one bit at a time using 1-bit CFB, although using one complete encryption of a block cipher for a single bit seems like a whole lot of work; a stream cipher might be a better idea. (Reducing the number of rounds of the block cipher to speed things up is not recommended [1269].) You can also use 64-bit CFB, or any n-bit CFB where n is less than or equal to the block size. Figure 9.9 shows 8-bit CFB mode working with a 64-bit block algorithm. A block algorithm in CFB mode operates on a queue the size of the input block. Initially, the queue is filled with an IV, as in CBC mode. The queue is encrypted and the left-most eight bits of the result are XORed with the first 8-bit character of the plaintext to become the first 8-bit character of the ciphertext. This character can now be transmitted. The same eight bits are also moved to the right-most eight bit positions of the queue, and all t...
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